The present invention relates to wells, either production or injection, having instruments permanently installed near the bottom thereof, and methods for installing such instruments.
It is often desirable to install instruments such as geophones or pressure or temperature sensors at the bottom of wells. A geophone located at the bottom of a well may be used for receiving signals in a vertical seismic profiling process or a tomographic imaging process Pressure or temperature sensors may be used to monitor conditions at the bottom of the well, typically in the producing or injection zone for long term control and maintenance purposes.
In the past, instruments have been simply inserted within the well casing on an appropriate cable for such purposes. However, such installations are subject to damage when other devices such as tubing or pumps are inserted into the same well casing. In the case of steam injection wells, the devices and electrical cable would be exposed to the injected steam typically at a temperature of 500.degree. F. Thus, installation of such devices within the casing exposes them to mechanical, chemical, and thermal damage.
To avoid the conditions within the well casing, instruments and the electrical cables required to connect them to the earth's surface have been attached to the outer surface of a well casing before insertion into the wellbore. While the armored cable used for these purposes can be strapped tightly to the well casing, and usually survives insertion of the well casing into the borehole, the instruments themselves are far more likely to be damaged or destroyed during the installation process. The instruments are of larger diameter than the cable and thus tend to be mechanically damaged as the casing is lowered down the borehole or when cement is pumped into the annulus between the casing and the borehole